A normally-closed valve is generally provided with a valve stem which opens and closes a fluid channel, a compression spring which biases the valve stem in a direction to close the fluid channel, and a piston body which is fitted in a cylinder in an air-tight fashion to be movable therein to thereby form a pressure chamber for moving the valve stem in a valve opening direction against the compression spring. The maximum valve-opening of this type of normally-closed valve can be adjusted by controlling the limit of movement of the piston body in the valve opening direction thereof. However, in this conventional type of normally-closed valve, since the flow rate is adjusted simply by adjusting the axial position of a stopper which is screw-engaged with the cylinder, the valve opening is determined by the pitch of the screw and the angle of rotation of the stopper, and accordingly, it is difficult to make a fine adjustment to the flow rate.